The present invention relates generally to extracorporeal blood treatment. More particularly the invention relates to a blood treatment apparatus according to the preamble of claim 1.
A conventional single-needle blood treatment apparatus, for instance a hemodialysis system or a hemodiafiltration system, contains a dialysis fluid circuit and a blood circuit with one or two blood pumps. For patient security reasons, single-needle dialysis is advantageous in a self care setting. Namely, here, there is no risk for dislodgement of a venous needle and thereby loss of blood being pumped out unintentionally via an arterial needle. Additionally, fewer needle punctures to the patient blood access are required relative to dual-needle treatment. Generally, the single-needle system is also well suited for long lasting treatments, such as nocturnal treatments. Moreover, single-needle dialysis may be used when the patient blood access is defective.
The prior art includes a range of examples of solutions for single-needle blood treatment, as well as pump means adapted to such implementations. For example, U.S. Pat. No. 4,552,552 describes a dialysis pumping system for a single-needle dialysis apparatus with a dialyzer having blood and dialysate circuits, and wherein the blood inlets and outlets are joined by intake and outtake lines with at least one blood connection. The intake line has a driving pump and pump valves placed upstream and downstream of the blood pump. The blood pump unit has a generally stiff housing with a diaphragm therein walling off the space in the housing into a first chamber for blood and a second chamber for driving fluid that is joined up with the driving pump. A respective high and low pressure limiting valve means prevent pressure levels outside a given interval by venting the working chamber whenever the pressure falls outside predetermined threshold values.
U.S. Pat. No. 6,645,166 reveals a blood treatment device and disposable kit for a blood treatment device, e.g. a dialysis machine, which permits both single- and dual-needle operation. Here, a blood treatment unit has an inlet connected to a feed line and an outlet connected to a return line. The feed line has two parallel line branches, where a positive displacement pump is connected to a first line branch, and a negative displacement pump is connected to a second line branch. Moreover, a connection line is provided to produce a fluid connection between the outlet of the blood treatment unit and one of the two pumps. For single-needle operation, the feed and return lines are brought together and connected to a common needle.
U.S. Pat. No. 6,899,693 discloses a compact pulsating pumping unit including means suitable to draw blood from an intake connector in order to send it to an outlet connector. Said means are contained in an enclosure provided with valves connected to the inlet and the outlet. An elastic membrane here separates the enclosure into two domes. This allows a working fluid to act on one side of the membrane, such that the membrane acts on blood located on the opposite side. The membrane thereby controls the operation of an inlet valve and an outlet valve, such that blood is moved into respective out from a pumping chamber.
Although the above solutions may have specific beneficial characteristics, they fail to provide an overall optimal fluid flow in a blood treatment apparatus. Moreover, operating the apparatus requires pressure measurements on the blood side. Hence, the design of the apparatus is compelled to be relatively intricate, and handling the apparatus becomes impractical. This, in turn, renders the apparatus unsuitable for a self care setting, where convenient and fail-safe handling is very important. Furthermore, blood pressure measurements on the blood side are problematic due to the potential risk of infection and contamination of the blood via the pressure measuring means, e.g. due to blood residuals from earlier treatments.